If you are planning to spend more than 3 days in Japan, you can consider purchasing a Japan prepaid data SIM card with 5GB data for 10 days.
It costs 2,350 yen (approximately S$28). This is better than paying our local telcos for travel roaming packages.
The following is a step-by-step guide on how to complete an online purchase of a Japan prepaid SIM card (data only) from Singapore. And collect it at the airport upon arrival.
1) Check that your mobile device is compatible under Supported Devices.
2) Visit b-mobile VISITOR SIM.
3) Select 5GB / 10 days.
4) Select Airport Post Office, and click Next.
5) Read and click “OK” to agree to all the statements, and click Next.
6) Complete the Purchase form. As you will need to present your passport (as a form of identification) during collection, remember to input your full name found in your passport (under the Name field).
9) If you have opted for Airport post office, simply present your Order number and passport at the Airport post office to collect your package.
10) After inserting your SIM card, you may need to configure your mobile phone’s APN setting before you can start using it.
If you have any questions, do post it as a comment below and I will try to respond to it.